Second harmonic mode polarization inverted resonator consisting of PbTiO3 thin film

Tunable bulk acoustic wave (BAW) resonator filter have attracted attention in recent years due to their potential application to microwave communications. For example, high tunability of 4.4 % with electromechanical coupling coefficient of 10 % was reported in BiFeO₃-BaTiO₃ film resonators [1]. On the other hand, the harmonic mode resonation in polarization inverted multilayer provides one possible way of realizing large tenability. Usual polarization unidirectional single layer resonator operates at fundamental (first) mode whereas the resonator consisting of double layer with opposite polarization operates at second harmonic mode. Polarization inverted ferroelectric thin mulitlayer structure make it possible to achieve two-way switching electrically between the harmonic mode operations. However, experimental studies of these structures have not been reported.